Andean Geology 41 (2): 436-445. May, 2014 Andean Geology doi: 10.5027/andgeoV41n2-a0810.5027/andgeoV40n2-a?? formerly Revista Geológica de Chile www.andeangeology.cl GEOLOGICAL NOTE

First radiometric age (U-Pb, LA-ICP-MS, on detrital zircons) from the Punta Topocalma Formation: insights on Late Cretaceous marine deposition in central Chile

*Alfonso Encinas1, Wolfgang Stinnesbeck2, Víctor A. Valencia3

1 Departamento de Ciencias de la Tierra, Universidad de Concepción, Casilla 160-C, Concepción, Chile. [email protected] 2 Institut für Geowissenschaften, Ruprecht-Karls-Universität, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany. [email protected] 3 School of Earth and Environmental Sciences, Washington State University, Pullman, Washington 99164, USA. [email protected]

* Corresponding author: [email protected]

ABSTRACT. Upper Cretaceous marine rocks crop out along the Pacific coast of central and south-central Chile between 33° and 37°S. These strata constitute an important reference for the Upper Cretaceous of South America due to their diverse fossil fauna and flora. The type unit of these deposits is the Quiriquina Formation, near Concepción. This unit is considered Maastrichtian in age based on ammonites. Upper Cretaceous marine strata from other localities of central and south-central Chile are largely unstudied and their biostratigraphic ages are not precisely known. We present the first radiometric dating (U-Pb on detrital zircons) for Upper Cretaceous marine strata of the Chilean forearc at Punta Topocalma that indicates a probable depositional age of 71.9+0.9 Ma (latest Campanian-earliest Maastrichtian). Provenance analysis indicates that the source of sediments of the Punta Topocalma Formation was plutonic and volcano-sedimentary rocks from the Coastal Cordillera and the Central Depression of central Chile. The Lo Valle Formation, a volcano-sedimentary unit in the Central Depression, recorded deposition of the Upper Cretaceous volcanic arc that was coeval with marine sedimentation in the Topocalma area.

Keywords: Upper Cretaceous, Quiriquina Formation, Punta Topocalma Formation, U-Pb Geochronology.

RESUMEN. Primera datación radiométrica (U-Pb, LA-ICP-MS, en zircones detríticos) de la Formación Punta Topocalma: observaciones sobre la sedimentación marina durante el Cretácico Tardío en Chile central. Rocas marinas del Cretácico Tardío afloran a lo largo de la costa pacífica de Chile central y centro-sur entre los 33°-37°S. Estos estratos constituyen una importante referencia para el Cretácico Superior de Sudamérica debido a la diversidad de su fauna y flora fósil. La unidad tipo de estos depósitos es la Formación Quiriquina que aflora en los alrededores de Concepción y es considerada de edad Maastrichtiana sobre la base de ammonites. Depósitos marinos del Cretácico Tardío en otras localidades de Chile central y centro-sur han sido poco estudiados y sus edades bioestratigráficas no se han determinado con precisión. Presentamos la primera edad radiométrica (U-Pb en zircones detríticos) en estratos marinos del Cretácico Superior de Punta Topocalma. Esta indica una probable edad de depósito de 71,9+0,9 Ma (Campaniano terminal-Maastrichtiano basal). El análisis de proveniencia señala que la fuente del sedimento de la Formación Punta Topocalma fueron rocas plutónicas y volcano-sedimentarias de la cordillera de la Costa y en la depresión Intermedia de Chile central. La Formación Lo Valle, unidad volcano-sedimentaria que aflora en la depresión Intermedia, recibió sus aportes de un arco volcánico del Cretácico Tardío contemporáneo con la sedimentación marina en el área de Topocalma.

Palabras clave: Cretácico Superior, Formación Quiriquina, Formación Punta Topocalma, Geocronología U-Pb. Encinas et al. / Andean Geology 41 (2): 436-445, 2014 437

1. Introduction overlies plutonic and metamorphic upper Paleozoic rocks and underlies Paleogene fluvial to brackish Campanian?-Maastrichtian (Upper Cretaceous) strata (Stinnesbeck, 1986, 1996). This unit forms a marine rocks crop out along the Pacific coast of fining-upward succession deposited in a coastal to central and south-central Chile between Algarrobo shallow-marine environment that comprises, from (33°S) and the Arauco Peninsula (37°S) (Stinnesbeck, base to top, a transgressive conglomerate, an interval 1986) (Fig. 1). Upper Cretaceous marine deposits of coarse-grained sandstone with interbedded con- have also been recognized in boreholes drilled on the glomerate and coquina, and a fine-grained glauco- continental shelf at the same latitudes (Mordojovich, nitic sandstone to siltstone interval with calcareous 1981). These strata have been studied since the concretions (Stinnesbeck,1986; Buatois and Encinas, 19th century (e.g., D’Orbigny, 1842; Darwin, 1846; 2011). Based on ammonites, a Late Senonian age Philippi, 1887; Steinmann et al., 1895; Wilckens, 1904; was originally assigned to the Quiriquina Formation Wetzel, 1930; Biró-Bagóczky, 1982; Stinnesbeck, by Steinmann (1895). However, Stinnesbeck (1986, 1986; Salazar et al., 2010; Buatois and Encinas, 1996) and Salazar et al. (2010) restricted the age 2011) and constitute an important reference for the of the unit to the Early to Late Maastrichtian, also Upper Cretaceous of South America due to their based on ammonite occurrences. diverse fossil fauna and flora that includes bivalves, Upper Cretaceous marine strata from other gastropods, scaphopods, cephalopods, crustaceans, localities of central and south-central Chile are birds, plesiosaurs, mosasaurs, turtles, fish, pollen, largely unstudied and their biostratigraphic ages and wood (for references see Salazar et al., 2010; are not precisely known (Fig. 1). They have been Buatois and Encinas, 2011). reported in the following localities: 1. the Arauco Most studies on Upper Cretaceous marine deposits peninsula (~37°30’S) where strata of the Quiriquina have been carried out on the Quiriquina Forma- Formation were identified in small outcrops and tion that crops out in the vicinity of Concepción wells drilled in the area by coal and oil companies (~36°45’S) (Fig. 1). Biró-Bagóczky (1982) proposed (see Stinnesbeck, 1986 and references therein); 2. Las Tablas Bay on Quiriquina Island as a type sec- Chanco (~35°S), where local strata were defined tion for this lithostratigraphic unit and a section at as the Chanco Formation and assigned to the late Cocholgüe, on the coast of the bay of Concepción, as Campanian by Tavera (19881) based on stratigraphic a complementary paratype. The Quiriquina Formation correlations and fossil invertebrates. However, Suárez

FIG. 1. A. Localities with outcrops of Upper Cretaceous marine deposits along the coast of central and south-central Chile; B. Geologic map of the study area (modified from Servicio Nacional de Geología y Minería, 2002; Encinas et al., 2006).

1 Tavera, J. 1988. Formación Quiriquina. Localidades para la formación. Estratotipos y fauna (latitudes 33°21’-37°50’). Unpublished monograph, Departamento de Geología, Universidad de Chile: 212 p. 438 First radiometric age (U-Pb, LA-ICP-MS, on detrital zircons) from the Punta Topocalma Formation... and Otero (2009) tentatively assigned the Chanco clasts are abundant at the top of the succession. strata to the Maastrichtian because their facies and Carbonate concretions of diagenetic origin are locally fossil content are similar to those identified in the abundant. The unit contains ammonites, bivalves, Quiriquina Formation; 3. Punta Topocalma (~34°S) fishes, reptiles, and wood fragments that are up to where they were defined as the Punta Topocalma one meter long (Pérez and Reyes, 1980; Suárez et al., Formation by Cecioni (1978) and assigned to the 2003).The poor preservation of sedimentary structures Upper Campanian based on ammonites (Pérez and prevents a refined sedimentologic interpretation. Reyes,1980); 4. Algarrobo (~33°S) where they were However, the presence of well-sorted sandstone with defined as the Estratos de la Quebrada Municipali- relatively abundant large wood fragments suggests a dad by Gana et al. (1996) and assigned to the early shallow-marine environment. Thin intercalations of Maastrichtian by Levi and Aguirre (1966) based on conglomerate and coquina are interpreted as storm ammonites, and by Suárez and Marquardt (2003) deposits. Pumice clasts in the upper part of the based on strontium isotope stratigraphy. succession were probably originated by episodes of The Quiriquina Formation is biostratigraphically explosive volcanism in the arc domain to the east. constrained to the Maastrichtian in its type sections around the bay of Concepción (e.g., Las Tablas, 3. U-Pb Geochronology Cocholgüe, Tomé; Stinnesbeck 1986, 1996; Salazar et al., 2010), but the precise ages of potentially One sample, consisting of ~10 kg of medium- correlative Late Cretaceous units to the north and grained sandstone with abundant pumice clasts, south of Concepción (Arauco, Chanco, Algarrobo, was selected for U-Pb zircon geochronology. Heavy and Punta Topocalma) are less well known and it mineral concentrates of the <350 µm fraction were remains unclear to date whether deposition in these separated using traditional techniques at ZirChron localities was strictly coeval or may have initiated LLC, Tucson Arizona. A split of zircons from the earlier, during the Campanian (e.g., Pérez and non-magnetic fraction was mounted in a 1’ epoxy Reyes, 1980; Biró-Bagóczky, 1982; Tavera, 1988). ring and slightly ground and polished previous to The presence of abundant pumice clasts in Upper laser ablation analysis. Cretaceous marine strata at Punta Topocalma prompted LA-ICP-MS U-Pb analyses were conducted at us to carry out U-Pb (LA-ICPMS) geochronological Washington State University prior to CL imaging analyses on detrital zircons. Here we present the first (University of Idaho) using a New Wave Nd:YAG radiometric age from Upper Cretaceous marine deposit UV 213-nm laser coupled to a ThermoFinnigan of the Chilean forearc basin and discuss possible Element 2 single collector, double-focusing, stratigraphic implications for the regional geology. magnetic sector ICP-MS. Operating procedures and parameters are a modification of Chang et al. 2. The Punta Topocalma Formation (2006). Laser spot size and repetition rate were 30 nm and 10 Hz, respectively. He and Ar carrier The Punta Topocalma Formation was defined by gases delivered the sample aerosol to the plasma. Cecioni (1978) in the homonymous locality (~34°S; Each analysis consisted of a short blank analysis Fig. 1). The unit at the type section is ~16 m thick followed by 250 sweeps through masses 204, 206, and overlies Paleozoic granitoids (Fig. 2). The upper 207, 208, 232, 235, and 238, taking approximately contact is a mild angular unconformity with marine 30 seconds. Time-independent fractionation was Miocene sandstone and siltstone of the Navidad corrected by normalizing U-Pb and Pb/Pb ratios Formation (Tavera, 1979; Encinas et al., 2006), to zircon standards (Chang et al., 2006). For this which is in turn overlain by cross-bedded sandstone study we used two zircon standards: Plesovice, with interpreted as Pleistocene? eolian paleodune deposits. an age of 338 Ma (Slama et al., 2008) and FC-1, The Topococalma Formation comprises a basal with an age of 1,099 Ma (Paces and Miller, 1993). interval, ~0.5 m thick, of fossiliferous conglomerate U-Pb ages and plots were calculated using Isoplot and locally very coarse sandstone, overlain by (Ludwig, 2003) and systematic and analytic errors ~15 m of green to yellow, well-sorted, medium- (2σ) were included. grained massive sandstone with scarce thin-bedded Zircon crystals in the sample analyzed are mainly intercalations of conglomerate and coquina. Pumice magmatic based on the Th/U ratio (1.0-0.4:1), Encinas et al. / Andean Geology 41 (2): 436-445, 2014 439

FIG. 2. Punta Topocalma section. Grain size: cl: clay; sil: silt; vfs: very fine sandstone; fs: fine s.; ms: medium s.; cs: coarse s.; vcs: very coarse s.; gg: gravel (granules); gp: gravel (pebbles); gc: gravel (cobbles); gb: gravel (boulders). The position of the U-Pb sample is indicated in the column. oscillatory and sector zoning, and morphology. The maximum depositional age of the Punta Zircons are pink colored and crystals mostly prismatic Topocalma Formation sample is ~71.9±0.9 Ma in shape, CL image shows predominantly long and (2 sigma, n=42) (Fig. 4). An abundant Mesozoic main thin zircons with broad to narrow oscillatory growth detrital zircon population is present and ranges from zoning (3-6:1 c/a axial ratio), which is common in 68-75 Ma (53% of the dated zircons). Other peak evolved volcanic rocks (Fig. 3). Detrital zircon grains populations show ages of ~89-105 Ma (8%), ~288- used here, however, were randomly selected and not 314 Ma (22%) and 321-352 Ma (10%). Single analyses by shape, size, clarity, or other attributes. at 572 Ma and 1,086 Ma are also present (Fig. 4). 440 First radiometric age (U-Pb, LA-ICP-MS, on detrital zircons) from the Punta Topocalma Formation...

4. Discussion

The age of Upper Cretaceous marine rocks of the Chilean forearc is mainly based on the study of ammonites from the Quiriquina Formation in the area of Concepción bay. In this unit, the assemblage is exceptionally diverse (30 taxa assigned to 17 genera) and shows affinities with Indo-Pacific and European assemblages (Stinnesbeck, 1986; Salazar et al., 2010). Biró-Bagóczky (1982) proposed a Campanian-Maastrichtian age for the formation, but subsequently, Stinnesbeck (1986, 1996) and Salazar et al. (2010) restricted the age of the Quiriquina Formation to the Maastrichtian. Salazar et al. (2010) refined the biostratigraphic scheme proposed by Stinnesbeck (1986) and divided the Quiriquina Formation into three biozones: 1. the Baculites anceps biozone, assigned to the late Early FIG. 3. Cathodoluminiscence image from the analyzed zircons. Maastrichtian; 2. the Eubaculites carinatus biozone,

FIG. 4. U-Pb plots from analyzed sample including the Tera-Wasseburg diagram (right inset), the probability density plot with the main age peaks and the youngest age calculated with the Tuff-Zirc algorithm (Ludwig, 2003). Encinas et al. / Andean Geology 41 (2): 436-445, 2014 441 which is further divided into the Menuites fresvil- (1980) were briefly revised by Stinnesbeck (1986) lensis subzone (early Late Maastrichtian) and the who was given access to the collection at Servi- Kitchinites (K.) darwini subzone (middle to late Late cio Nacional de Geología y Minería, in Santiago. Maastrichtian); and 3. a biozone without Baculitids Stinnesbeck (1986, p. 124) states the presence tentatively assigned to the latest Late Maastrichtian. of Maorites aff. tenuicostatus, Nostoceras sp., The Quiriquina ammonite assemblage correlates well Baculites sp., Inoceramus (Endocostea) biroi, Pac- with the top of the López de Bertodano Formation itrigonia hanetiana, Buchotrigonia topocalmensis, in Seymour Island, Antarctica, the Miria Formation Cardium (Bucardium) acuticostatum, Aphrodina in Western Australia, the top of Valudayur Forma- quiriquinae, ?Mytilus sp., Nucula aff. N. (Leionucula) tion in the Pondicherri district of southern India, ceciliana, Perna sp., Turbo ovallei, and Calyptraea sp. and sections in the Biscay region in SW France and Suárez et al. (2003) also noted the occurrence of Spain. These units are mainly Late Maastrichtian Centrophoroides sp., Charcharias sp., Ischirhiza in age, which is also indicated by the presence of chilensis sp., Teleostei indet., and Elasmosauridae indet. planktonic foraminifers assigned to the Gansserina The interpretation of Pérez and Reyes (1980) gansseri and Abathomphalus mayaroensis zones that the Punta Topocalma Formation is older than (Stinnesbeck, 1986, 1996; Salazar et al., 2010 and the classical sections of the Quiriquina Formation is references therein). based on the absence of unequivocal Maastrichtian Direct correlation between the Quiriquina index fossils, such as Eubaculites carinatus, Fresvillia Formation and reference successions for the Maas- constricta, Hoploscaphites constrictus, Pachydiscus. trichtian stage in Europe, however, must be taken (P.) jacquoti, and Menuites fresvillensis. These with caution as there is no world-wide ammonite ammonites are characteristic faunal elements in zonation for this period and planktonic index fossils the type sections of the Quiriquina Formation at such as foraminifers or coccolithophorids are not Las Tablas and at Cocholgüe and are well known preserved in strata of the Quiriquina Formation and from Maastrichtian strata outside South America correlative units (Stinnesbeck, 1986, 1996; Salazar (e.g., Europe). However, they have never been et al., 2010). In addition, the use of independent reported in the Punta Topocalma Formation. The radiometric dating methods to test the accuracy of faunal ranges of the Punta Topocalma ammonites correlations based on ammonite biostratigraphy is Gunnarites, Grossouvrites, and Baculites are not hampered, in the area of Concepción bay, by the well known at generic level, but clearly include absence of interbedded volcanic rocks. both the Campanian and Maastrichtian, at least As noted above, deposition of Upper Cretaceous for the Austral realm (Patagonia, Antarctica) marine rocks in other localities of the Chilean (Macellari, 1985, 1988; Stinnesbeck et al., 2012). forearc could have started earlier, in the Campan- Nostoceras, determined by Stinnesbeck (1986, p. 124) ian or the Early Maastrichtian (Levi and Aguirre, in the Punta Topocalma collection of Pérez and 1966; Pérez and Reyes, 1980; Tavera, 1988; Suárez Reyes (1980), is known to range from the Late and Marquardt, 2003). Studies on the precise age Campanian to Early Maastrichtian (Ifrim et al., of these successions, however, are scarce and their 2004). Tentatively, Maorites aff. tenuicostatus conclusions must be taken with some caution as they (determined by Stinnesbeck, 1986, p. 124) may were likely skewed by insufficient fossil sampling correspond to Maorites densicostatus (Marshall; and sparse documentation. The Punta Topocalma see Salazar et al., 2010), a taxon described from Formation was assigned to the Late Campanian by the Santonian to Maastrichtian of New Zealand; Pérez and Reyes (1980) based on the presence of elsewhere in the southern South Pacific region. the ammonites Gunnarites sp. and Grossouvrites sp. M. densicostatus may be restricted to the Maastrichtian Pérez and Reyes (1980) cited the presence of the (Salazar et al., 2010). following taxa in strata of the Punta Topocalma The bivalve assemblage at Punta Topocalma Formation: Baculites sp., Gunnarites sp., Grossouv- includes trigoniids and inoceramids which have reites sp., Buchotrigonia (B.) topocalmensis sp. nov., variously been interpreted to be of biostratigraphical Pacitrigonia banetiana (D’ Orbigny), Cardium significance. Buchotrigonia (B.) topocalmensis, a (B.) acuticostatum (D’ Orbigny) and lnoceramus characteristic faunal component at Punta Topocalma, sp. The fossils collected by Pérez and Reyes was never identified in the Concepción area, while 442 First radiometric age (U-Pb, LA-ICP-MS, on detrital zircons) from the Punta Topocalma Formation...

Pacitrigonia hanetiana is known from both localities. Cretaceous zircon population. The ammonites reported Inoceramids are abundant throughout the Late by Pérez and Reyes (1980) were obtained from the Cretaceous, but a global extinction of this important basal conglomerate of the Punta Topocalma section bivalve genus was registered within the Early and must therefore be older than the rock sample Maastrichtian (MacLeod et al., 1996). The Punta used for U-Pb geochronology, which was obtained Topocalma species determined as Inoceramus sp. from the upper part of the succession. On the other by Pérez and Reyes (1980) was assigned to hand, thickness of the Punta Topocalma section is I. (Endocostea) biroi by Stinnesbeck (1986, p. 124). only ~16 m and depositional rates for shallow-marine This taxon was established by Stinnesbeck (op. cit.) settings are generally high. Therefore, the difference in the basal Quiriquina Formation of the Concepcion in age between the base and top of the succession area (e.g., Las Tablas), where it is constrained to may not differ significantly. The 71.9+0.9 Ma the unit of ‘yellow cross-bedded sandstone’ near U-Pb age reported here does neither prove nor re- the base of the formation. I. (Endocostea) biroi is fute the late Campanian age assigned by Pérez and there associated with Baculites anceps, an Early Reyes (1980) for the Punta Tococalma Formation. to Late Maastrichtian taxon (Salazar et al., 2010). The sample analyzed by U-Pb geochronology According to these arguments, the Punta Topo- shows four distinct detrital zircon populations of calma Formation could be Late Campanian or Early ~68-75 Ma (Maastrichtian- Campanian), ~89-105 Ma Maastrichtian in age. Faunal differences between (Coniacian-Albian), ~288-314 Ma (Artinskian- the Punta Topocalma and the Quiriquina formations Moskovian), and 321-352 (Bashkirian-Tournaisian) are clearly stated by the presence of Buchotrigonia which allows for some paleogeographic interpre- topocalmensis and Nostoceras in the first unit and tations. Radiometric ages of 308±15 Ma (Rb/Sr), may reflect earlier deposition of the Punta Topo- 299±10 Ma (U-Pb), and 309 Ma (U-Pb) were calma Formation, or a stratigraphic overlap with obtained from Paleozoic granitoids that crop out the basal Quiriquina Formation at Concepcion bay in the Coastal Cordillera of central Chile (Godoy (e.g., the unit of yellow cross-bedded sandstone at and Loske, 1988; Wall et al., 1996 and references Las Tablas section). therein). These plutonic rocks are the most likely Alternatively, however, other causes may also source for the Permian-upper Carboniferous popula- exist to explain faunal differences between the two tions of detrital zircons from the Punta Topocalma outcrop areas, such as insufficient sampling and poor section. The oldest group of zircons (321-352) fossil preservation at Punta Topocalma, or differences could have also been derived from upper Paleozoic in paleoecological setting. Future paleontological metamorphic rocks that crop out in the same area and biostratigraphical research is clearly needed for (Wall et al., 1996). Punta Topocalma to decide whether these sediments K-Ar radiometric ages between 118 and 91 Ma are Early Maastrichtian in age and thus coeval to where obtained from plutonic rocks (granitoids and the basal Quiriquina Formation, or Late Campanian gabbros) of the western Coastal Cordillera near and thus slightly older. Valparaíso (~33°S) (Gana et al., 1996). An age of These uncertainties regarding the biostratigraphi- 107±0.62 Ma (40Ar/39Ar) was obtained for granitoids cal interpretation of the Punta Topocalma section from the eastern Coastal Cordillera, south of Santiago are well reflected by the U-Pb radiometric age of (~33°30’S, Sellés and Gana, 2001). Radiometric 71.9+0.9 Ma for the youngest zircon population of (U-Pb) ages between 106 and 110 Ma were obtained the sample analyzed in this study. This age is close by Wall et al. (1999) from basal strata of the Las to the Campanian-Maastrichtian boundary which Chilcas Formation, a volcano-sedimentary unit in the has been established at 72.1±0.2 Ma (Cohen et al., eastern part of the Coastal Cordillera near Santiago. 2013). The Punta Topocalma age of 71.9+0.9 Ma is In addition, Martínez-Pardo et al. (1994) assigned considered as a maximum depositional age because an Albian age to a limestone unit that forms part it was calculated from detrital zircons. However, of this formation, based on benthic foraminifers. the rock sample was obtained from an interval with Thus, the ~89-105 Ma zircon population from the abundant pumice clasts which were likely derived Punta Topocalma Formation was likely derived from from explosive volcanism coeval with sediment plutonic rocks of the Coastal Cordillera of central deposition and are the probable source of the Late Chile, or from volcano-sedimentary strata of the Las Encinas et al. / Andean Geology 41 (2): 436-445, 2014 443

Chilcas Formation exposed in the eastern Coastal en su localidad tipo en la Isla Quiriquina, 36º35’ Cordillera and Central Valley. Lat. S, Chile, Sudamérica, con un perfil complemen- Three 40Ar/39Ar ages of 72.4±1.4, 71.9±1.4, and tario en Cocholgüe. In Congreso Geológico Chileno 71.4±1.4 Ma were obtained by Gana and Wall (1997) No. 3, Actas 3: A29-64. Concepción. from tuffs and ignimbrites of the Lo Valle Formation, a Buatois, L.A.; Encinas, A. 2011. Ichnology, sequence volcano-sedimentary unit that crops out in the Central stratigraphy and depositional evolution of an Upper Depression in the vicinity of Santiago. In addition, Cretaceous rocky shoreline in central Chile: Bioerosion a K-Ar age of 72±3 Ma was obtained by Sellés and structures in a transgressed metamorphic basement. Gana (2001) from volcanic rocks (lavas) that crop out Cretaceous Research 32: 203-212. in the eastern Coastal Cordillera south of Santiago Cecioni, G. 1978. Petroleum possibilities of the Darwin’s (~34°S), but these were assigned to the upper Las Navidad Formation near Santiago, Chile. Publicación Chilcas Formation by the authors. These radiometric Ocasional del Museo Nacional de Historia Natural, ages are similar to, or even indistinguishable from Chile 25: 3-28. the U-Pb age of 71.9+0.9 Ma obtained here for the Chang, Z.; Vervoort, J.D.; Knaack, C.; McClelland, Punta Topocalma Formation. We therefore suggest W.C. 2006. U-Pb dating of zircon by LA-ICP-MS. that the Lo Valle and the upper Las Chilcas forma- Geochemistry, Geophysics, Geosystems 7 (5): 1-14. tions were deposited coeval to marine sediments of Cohen, K.M.; Finney, S.M.; Gibbard, P.L.; Fan, J.X. the Punta Topocalma Formation. 2013. The ICS International Chronostratigraphic Chart. Episodes 36 (3): 199-204. 5. Conclusions Darwin, C. 1846. Geological Observations on South America. Smith Elder and Co.: 279 p. London. The first radiometric dating (U-Pb on detrital D’Orbigny, A. 1842. Voyage dans l’Amérique méridi- zircons) for Upper Cretaceous marine strata of onale 1826-1833, tome 3, 3e partie, Géologie (289, the Chilean forearc was carried out at Punta Topo- 10 pls); 4e partie Paléontologie (188, 22 pls). Paris. calma and indicates a probable depositional age of Encinas, A.; Le Roux, J.P.; Buatois, L.A.; Nielsen, S.N.; 71.9+0.9 Ma (latest Campanian-earliest Maas- Finger, K.L.; Fourtanier, E.; Lavenu, A. 2006. Nuevo trichtian). Provenance analysis based on the age of esquema estratigráfico para los depósitos marinos mio- detrital zircon populations suggests that the source pliocenos del área de Navidad (33°00’-34°30’S), Chile of sediments of the Punta Topocalma Formation was central. Revista Geológica de Chile 33 (2): 221-246. plutonic and volcano-sedimentary rocks from the Gana, P.; Wall, R.; Gutiérrez, A. 1996. Mapa Geológico Coastal Cordillera and the Central Depression of del área de Valparaíso-Curacaví, Región de Valparaíso central Chile. The Lo Valle Formation, a volcano- y Región Metropolitana. Servicio Nacional de Ge- sedimentary unit in the Central Depression, recorded ología y Minería, Mapas Geológicos 1: 20 p., escala deposition of the Upper Cretaceous volcanic arc that 1:100.000. Santiago. was coeval with marine sedimentation in the Punta Gana, P.; Wall, R. 1997. Evidencias geocronológicas Topocalma area. 40Ar/39Ar y K-Ar de un hiatus Cretácico Superior-Eoceno en Chile central (33-33°30’S). Revista Geológica de Acknowledgments Chile 24 (2): 145-163. This research was funded by Fondecyt Project num- Godoy, E.; Loske, W. 1988. Tectonismo sinplutónico de ber 1110914 of Conicyt. Research in Chile by WS was dioritas Jurásicas al sur de Valparaíso: datos U-Pb funded by the Deutsche Forschungsgemeinschaft (STI sobre la ‘fase Quintay’. Revista Geológica de Chile 128/15) and the Bundesministerium für Wissenschaft 15 (2): 119-127. und Forschung (BMBF CHL10/A09). The authors are Ifrim, C.; Stinnesbeck, W.; López-Oliva, J.G. 2004. grateful to Dr. Ch. Salazar and an anonymous reviewer Maastrichtian cephalopods from the Mendez Forma- for their helpful suggestions and constructive comments. tion at Cerralvo, Nuevo León, North-Eastern Mexico. Palaeontology 47 (6): 1-53. References Levi de Valenzuela, B.; Aguirre, L. 1966. El Conglome- rado de Algarrobo y su relación con las formaciones Biró-Bagóczky, L. 1982. Revisión y redefinición de los del Cretácico Superior de Chile Central. Instituto de ‘Estratos de Quiriquina’, Campaniano-Maastrichtiano, Investigaciones Geológicas 17: 417-431. 444 First radiometric age (U-Pb, LA-ICP-MS, on detrital zircons) from the Punta Topocalma Formation...

Ludwig, K.R. 2003. User’s Manual for Isoplot 3.00, A y Minería, Geología Básica 75, 1 mapa en 3 hojas, Geochronological Toolkit for Microsoft Excel. Berkeley escala 1:1.000.000. Santiago. Geochronology Center Special Publication 4: 70 p. Slama, J.; Kosler, I.; Condon, D.; Crowley, J.; Gerdes, A.; Macellari, C.E. 1985. Paleobiografía y Edad de Maorites- Hanchar, J.; Horstwood, M.; Morris, G.A.; Nasdala, L.; Gunnarites (Ammonoidea) del Cretácico Superior de Norberg, N.; Schaltegger, U.; Schoene, B.; Tubrett, la Antártica y Patagonia. Ameghiniana 21: 223-242. M.N.; Whitehouse, M.J. 2008. Plešovice zircon- A new Macellari, C.E. 1988. Late Cretaceous Kossmaticeratidae natural reference material for U-Pb and Hf isotopic (Ammonoidea) from the Magallanes Basin, Chile. microanalysis. Chemical Geology 249 (1-2): 1-35. Journal of Paleontology 62: 889-905. Steinmann, G. 1895. Die Cephalopoden der Quiriquina- MacLeod, K.G.; Huber, B.T.; Ward, P.D. 1996. The Schichten. Neues Jahrbuch für Mineralogie, Geologie biostratigraphy and paleobiogeography of Maastrich- und Paläontologie 10: 64-94. tian inoceramids. In The Cretaceous-Tertiary Event Steinmann, G.; Deeke, W.; Möricke, W. 1895. Das Alter and other Catastrophes in Earth History (Ryder, G.; und die Fauna der Quiriquina Schichten in Chile. Fastovsky, D.E.; Gartner, S.; editors). Geological Neues Jahrbuch für Mineralogie, Geologie und Society of America, Special Paper 307: 361-373. Paläontologie: 118 p. Martínez-Pardo, R.; Gallego, A.; Martínez-Guzmán, R. Stinnesbeck, W. 1986. Zu den faunistischen und palökolo- 1994. Middle Albian marine planktonic microfos- gischen Verhältnissen in der Quriquina Formation sils from the Santiago basin, central Chile: their (Maastrichtium) Zentral-Chiles. Palaeontographica depositional and paleogeographic meaning. Revista A194: 99- 237, 1-16 pl. Geológica de Chile 21 (2): 173-187. Stinnesbeck, W. 1996. Ammonite Extinctions and Envi- Mordojovich, C. 1981. Sedimentary basins of Chilean ronmental Changes across the Cretaceous-Tertiary Pacific offshore. In Energy resources of the Pacific Boundary in Central Chile. In The Cretaceous-Tertiary region. American Association of Petroleum Geolo- Boundary Mass Extinction: Biotic and Environmental gists Special Volumes, Studies in Geology 12: 63-68. Events (MacLeod, N.; Keller, G.; editors), Norton Paces, J.B.; Miller, J.D. 1993. Precise U-Pb ages of Duluth Press: 289-302. New York. complex and related mafic intrusions, northeastern Stinnesbeck, W.; Ifrim, C.; Salazar, C. 2012. The last Minnesota; geochronological insights to physical, Cretaceous ammonites in Latin America. Acta Pa- petrogenetic, paleomagnetic, and tectonomagmatic leontologica Polonica 57 (4): 717-728. processes associated with the 1.1 Ga midcontinent Suárez, M.E.; Marquardt, C. 2003. Revisión preliminar rift system. Journal of Geophysical Research 98 (B8): de las faunas de peces elasmobranquios del Meso- 13997-14013. doi: 10.1029/93JB01159. zoico y Cenozoico de Chile. In Congreso Geológico Pérez-D’Angelo, E.; Reyes, R. 1980. Buchotrigonia (Bu- Chileno No. 10, Sesión temática 3, Paleontología, chotrigonia) topocalmensis (Trigoniidae; Bivalvia) Actas CD-Rom: 9 p. Concepción. del Cretácico Superior de Chile. Revista Geológica Suárez, M.E.; Quinzio, L.A.; Fritis, O.; Bonilla, R. 2003. de Chile 9: 37-55. Aportes al conocimiento de los vertebrados marinos Philippi, R.A. 1887. Die tertiären und quartären Ver- de la Formación Quiriquina. In Congreso Geológico steinerungen Chiles. Brockhaus: 266 p. 58 pls. Leipzig. Chileno No. 10, Sesión temática 3, Paleontología, Salazar, C.; Stinnesbeck, W.; Quinzio-Sinn, L.A. 2010. Actas CD-Rom: 9 p. Concepción. Ammonites from the Maastrichtian (Upper Creta- Suárez, M.E.; Otero, R.A. 2009. Nuevos hallazgos de ceous) Quiriquina Formation in central Chile. Neues vertebrados marinos en el Campaniano-Maastrichtiano Jahrbuch Geologie und Paläontologie Abhandlungen de Loanco, VII Región. In Simposio de Paleontología 257: 181-236. en Chile No. 1 (Rubilar, A.; Rubilar-Rogers, D.; Gut- Sellés, D.; Gana, P. 2001. Geología del área Talagante- stein, C.; editores). Libro de Actas: 78-82. Santiago. San Francisco de Mostazal, Regiones Metropolitana Tavera, J. 1979. Estratigrafía y Paleontología de la de Santiago y del Libertador General Bernardo Formación Navidad, Provincia de Colchagua, Chile O’Higgins. Servicio Nacional de Geología y Minería, (Lat 30°50’-34°S). Boletín del Museo Nacional de Serie Geología Básica 74: 30 p., escala 1:100.000. Historia Natural de Chile 36 (5-10): 176 p. Santiago. Wall, R.; Gana, P.; Gutiérrez, A. 1996. Área de San An- Servicio Nacional de Geología y Minería, 2002. Mapa tonio- Melipilla, Regiones de Valparaíso, Metropoli- geológico de Chile. Servicio Nacional de Geología tana y del Libertador General Bernardo O’Higgins. Encinas et al. / Andean Geology 41 (2): 436-445, 2014 445

Servicio Nacional de Geología y Minería, Mapas Wetzel, W. 1930. Die Quiriquina Schichten als Sediment Geológicos 2: 20 p., escala 1:100.000. Santiago. und paläontologisches Archiv. Palaeontographica Wall, R.; Sellés, D.; Gana, P. 1999. Área Til Til-Santi- 73: 49-101. ago, Región Metropolitana. Servicio Nacional de Wilckens, O. 1904. Revision der Fauna der Quiriquina Geología y Minería, Mapas Geológicos 11, escala Schichten. Neues Jahrbuch für Mineralogie, Geologie 1:100.000. Santiago. und Paläontologie Beilage-Band 18: 181-284.

Manuscript received: July 30, 2013; revised/accepted: November 21, 2013; available online: November 22, 2013.